Prediction of surface topography anomalies during radial immersion micromilling

• Mechanisms of surface anomalies formation in micromilling identified for a first time. • Original and complex micromilled surface topography hybrid HMT/Z-Map model. • Important role of corner radius, helix angle and kinematics on surface anomalies. • Accurate model for prediction of shape and geometry of surface anomalies. • Proposed model is more precise for anomalies modeling than models without backcutting. The reliable modelling of 3D surface topography in micromilling processes remains a critical challenge in precision manufacturing. However, the mechanisms behind the formation of machined surface anomalies, resulting from interactions between tool geometry and the flexibility of the tool-spindle system, have not yet been fully recognised and characterised in the literature. This study introduces, for the first time, an original 3D surface topography model for radial immersion micromilling, accounting for machined surface anomalies induced by tool tip deflection variations that result from the geometry of the micromilling cutter and tool-spindle system flexibility. In the initial stage of this work, a novel 3D surface topography model based on a hybrid homogeneous matrix transformation/Z-map (HMT/Z-map) approach was developed, incorporating the trochoidal trajectory of the tool tip. This model was further enhanced to include the effects of tool-spindle system run-out. Subsequently, the influence of instant axial and radial tool tip deflections, derived from a tool-spindle system stiffness model, was integrated into the modelling process. As part of this stage, an original iterative algorithm was proposed to identify the instant tool position in the modelled cutting force equilibrium state. Finally, the developed hybrid HMT/Z-map model was extended to include the effects of backcutting mechanisms in the formation of machined surface topographies containing surface anomalies. In the next stage, the proposed model was validated through micromilling experiments using Inconel 718 alloy as the workpiece. The micromilling tests were performed on an ultra-precise prototype milling machine, SNTM CM–ZUT–1. The experiments involved radial immersion micromilling conducted under variable cutting conditions (radial cut depth, feed, and cutting speed) as well as different milling kinematics (up-milling and down-milling). The results demonstrated that during the down-micromilling process, performed with tools equipped with helical cutting edges and a rounded corner radius, machined surface anomalies appeared as bands with elevated machining marks compared to the surrounding areas. The proposed 3D surface topography model enables precise estimation of the geometrical parameters (heights and widths) of surface anomaly bands across a wide range of machining conditions, milling kinematics, and tool geometries.